Tuesday, 30 March 2010

Panasonic GH1 exposure, nightscenes

I have noted that the Panasonic GH1 consistently gives too dark exposures in night scenes, or more generally, in scenes with high contrast, large difference between the light and dark parts of the image.

Here is an example scene, shot with two different cameras. Panasonic GH1 top, and Pentax K10D bottom.

Panasonic GH1

Pentax K10D

Both cameras were set in "P" mode, auto white balance, and multi segment exposure metering. The field of view was 200mm (film camera equivalent), with aperture f/6.7, ISO 400. The JPEG images were used straight from the camera, with rescaling and a little bit of sharpening.

As you can see straight away, the Pentax exposure is much more usable, even if the white balance could have been better. But in terms of white balance, this is a very trick situation anyway, with artificial lights.

Let's compare the JPEG histograms, taken from the Gimp image processing software:

Here it is very apparent that the Pentax has a more useful exposure. The Panasonic exposure appears to be designed to avoid blown highlights, while the Pentax exposure puts more weight on preserving details in the shadows.

Highlight details

Let's see how the highlights compare. Here are 100% crop from the same area in both pictures:

Panasonic GH1

Pentax K10D

As is apparent, Panasonic exposes less, and hence is able to preserve more details in the highlights. However, to achieve this, a lot of detail in the darker parts of the picture, which makes up the most of the area, is lost.

Appendix

The lenses used were the Panasonic Lumix G HD 14-140mm f/4-5.8 @ 100mm, and the Pentax DA* 50-135mm f/2.8 @ 135mm. The camera was on tripod during both exposures. The exposures were around a couple of seconds, with image stabilization turned off. You can see that the Panasonic lens is much sharper, even if it is less stopped down. This is quite a feat for a 10x zoom. On the other hand, the Pentax lens is a faster lens, which implies other compromises in the design.